Add macOS menu bar agent mode

[realist-pessimist]

Summary

Adds a macOS menu bar mode that keeps Java Daemon Watcher alive after the main window is closed.

What changed

• runs as an accessory-style macOS app via LSUIElement
• creates a persistent NSStatusItem in the macOS menu bar
• opens a compact popover from the status item
• keeps a separate reopenable main window for the full app UI
• returns to menu-bar-only mode after the main window is closed
• adds an Open window action inside the popover
• tightens the popover/window layout so the compact view feels denser

New behavior

1. Launching the app opens the main window.
2. While the main window is visible, the app can behave like a regular desktop window.
3. Closing the main window does not quit the app.
4. The app remains available from the menu bar icon.
5. Clicking the menu bar icon opens the compact popover.
6. Open window restores the main window when needed.

Screenshots

Main window:

Menu bar icon:

Menu bar popover:

Validation

• built locally with xcodebuild -project JavaDaemonWatcher/JavaDaemonWatcher.xcodeproj -scheme JavaDaemonWatcher -configuration Debug build
• manually verified the flow: open window -> close window -> keep app in menu bar -> reopen from popover